Reimplement isPotentiallyReachable to make nocapture deduction much stronger.
Adds unit tests for it too.
Split BasicBlockUtils into an analysis-half and a transforms-half, and put the
analysis bits into a new Analysis/CFG.{h,cpp}. Promote isPotentiallyReachable
into llvm::isPotentiallyReachable and move it into Analysis/CFG.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@187283 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Analysis/AliasAnalysis.cpp b/lib/Analysis/AliasAnalysis.cpp
index 5be5613..b8b6d37 100644
--- a/lib/Analysis/AliasAnalysis.cpp
+++ b/lib/Analysis/AliasAnalysis.cpp
@@ -26,6 +26,7 @@
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/CaptureTracking.h"
+#include "llvm/Analysis/CFG.h"
#include "llvm/Analysis/Dominators.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/IR/BasicBlock.h"
@@ -361,26 +362,6 @@
}
namespace {
- /// Determine whether there is a path from From to To within a single
- /// function. Returns false only if we can prove that once 'From' has been
- /// executed then 'To' can not be executed. Conservatively returns true.
- static bool isPotentiallyReachable(const BasicBlock *From,
- const BasicBlock *To) {
- const unsigned MaxCheck = 5;
- const BasicBlock *Current = From;
- for (unsigned I = 0; I < MaxCheck; I++) {
- unsigned NumSuccs = Current->getTerminator()->getNumSuccessors();
- if (NumSuccs > 1)
- return true;
- if (NumSuccs == 0)
- return false;
- Current = Current->getTerminator()->getSuccessor(0);
- if (Current == To)
- return true;
- }
- return true;
- }
-
/// Only find pointer captures which happen before the given instruction. Uses
/// the dominator tree to determine whether one instruction is before another.
/// Only support the case where the Value is defined in the same basic block
@@ -402,7 +383,7 @@
// there is no need to explore the use if BeforeHere dominates use.
// Check whether there is a path from I to BeforeHere.
if (BeforeHere != I && DT->dominates(BeforeHere, I) &&
- !isPotentiallyReachable(BB, BeforeHere->getParent()))
+ !isPotentiallyReachable(I, BeforeHere, DT))
return false;
return true;
}
@@ -414,7 +395,7 @@
if (BeforeHere != I && !DT->isReachableFromEntry(BB))
return false;
if (BeforeHere != I && DT->dominates(BeforeHere, I) &&
- !isPotentiallyReachable(BB, BeforeHere->getParent()))
+ !isPotentiallyReachable(I, BeforeHere, DT))
return false;
Captured = true;
return true;
diff --git a/lib/Analysis/CFG.cpp b/lib/Analysis/CFG.cpp
new file mode 100644
index 0000000..a5ed21a
--- /dev/null
+++ b/lib/Analysis/CFG.cpp
@@ -0,0 +1,227 @@
+//===-- CFG.cpp - BasicBlock analysis --------------------------------------==//
+//
+// The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This family of functions performs analyses on basic blocks, and instructions
+// contained within basic blocks.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Analysis/CFG.h"
+
+#include "llvm/ADT/SmallSet.h"
+#include "llvm/Analysis/Dominators.h"
+#include "llvm/Analysis/LoopInfo.h"
+
+using namespace llvm;
+
+/// FindFunctionBackedges - Analyze the specified function to find all of the
+/// loop backedges in the function and return them. This is a relatively cheap
+/// (compared to computing dominators and loop info) analysis.
+///
+/// The output is added to Result, as pairs of <from,to> edge info.
+void llvm::FindFunctionBackedges(const Function &F,
+ SmallVectorImpl<std::pair<const BasicBlock*,const BasicBlock*> > &Result) {
+ const BasicBlock *BB = &F.getEntryBlock();
+ if (succ_begin(BB) == succ_end(BB))
+ return;
+
+ SmallPtrSet<const BasicBlock*, 8> Visited;
+ SmallVector<std::pair<const BasicBlock*, succ_const_iterator>, 8> VisitStack;
+ SmallPtrSet<const BasicBlock*, 8> InStack;
+
+ Visited.insert(BB);
+ VisitStack.push_back(std::make_pair(BB, succ_begin(BB)));
+ InStack.insert(BB);
+ do {
+ std::pair<const BasicBlock*, succ_const_iterator> &Top = VisitStack.back();
+ const BasicBlock *ParentBB = Top.first;
+ succ_const_iterator &I = Top.second;
+
+ bool FoundNew = false;
+ while (I != succ_end(ParentBB)) {
+ BB = *I++;
+ if (Visited.insert(BB)) {
+ FoundNew = true;
+ break;
+ }
+ // Successor is in VisitStack, it's a back edge.
+ if (InStack.count(BB))
+ Result.push_back(std::make_pair(ParentBB, BB));
+ }
+
+ if (FoundNew) {
+ // Go down one level if there is a unvisited successor.
+ InStack.insert(BB);
+ VisitStack.push_back(std::make_pair(BB, succ_begin(BB)));
+ } else {
+ // Go up one level.
+ InStack.erase(VisitStack.pop_back_val().first);
+ }
+ } while (!VisitStack.empty());
+}
+
+/// GetSuccessorNumber - Search for the specified successor of basic block BB
+/// and return its position in the terminator instruction's list of
+/// successors. It is an error to call this with a block that is not a
+/// successor.
+unsigned llvm::GetSuccessorNumber(BasicBlock *BB, BasicBlock *Succ) {
+ TerminatorInst *Term = BB->getTerminator();
+#ifndef NDEBUG
+ unsigned e = Term->getNumSuccessors();
+#endif
+ for (unsigned i = 0; ; ++i) {
+ assert(i != e && "Didn't find edge?");
+ if (Term->getSuccessor(i) == Succ)
+ return i;
+ }
+}
+
+/// isCriticalEdge - Return true if the specified edge is a critical edge.
+/// Critical edges are edges from a block with multiple successors to a block
+/// with multiple predecessors.
+bool llvm::isCriticalEdge(const TerminatorInst *TI, unsigned SuccNum,
+ bool AllowIdenticalEdges) {
+ assert(SuccNum < TI->getNumSuccessors() && "Illegal edge specification!");
+ if (TI->getNumSuccessors() == 1) return false;
+
+ const BasicBlock *Dest = TI->getSuccessor(SuccNum);
+ const_pred_iterator I = pred_begin(Dest), E = pred_end(Dest);
+
+ // If there is more than one predecessor, this is a critical edge...
+ assert(I != E && "No preds, but we have an edge to the block?");
+ const BasicBlock *FirstPred = *I;
+ ++I; // Skip one edge due to the incoming arc from TI.
+ if (!AllowIdenticalEdges)
+ return I != E;
+
+ // If AllowIdenticalEdges is true, then we allow this edge to be considered
+ // non-critical iff all preds come from TI's block.
+ while (I != E) {
+ const BasicBlock *P = *I;
+ if (P != FirstPred)
+ return true;
+ // Note: leave this as is until no one ever compiles with either gcc 4.0.1
+ // or Xcode 2. This seems to work around the pred_iterator assert in PR 2207
+ E = pred_end(P);
+ ++I;
+ }
+ return false;
+}
+
+// LoopInfo contains a mapping from basic block to the innermost loop. Find
+// the outermost loop in the loop nest that contains BB.
+static const Loop *getOutermostLoop(LoopInfo *LI, const BasicBlock *BB) {
+ const Loop *L = LI->getLoopFor(BB);
+ if (L) {
+ while (const Loop *Parent = L->getParentLoop())
+ L = Parent;
+ }
+ return L;
+}
+
+// True if there is a loop which contains both BB1 and BB2.
+static bool loopContainsBoth(LoopInfo *LI,
+ const BasicBlock *BB1, const BasicBlock *BB2) {
+ const Loop *L1 = getOutermostLoop(LI, BB1);
+ const Loop *L2 = getOutermostLoop(LI, BB2);
+ return L1 != NULL && L1 == L2;
+}
+
+static bool isPotentiallyReachableSameBlock(const Instruction *A,
+ const Instruction *B,
+ LoopInfo *LI) {
+ // The same block case is special because it's the only time we're looking
+ // within a single block to see which comes first. Once we start looking at
+ // multiple blocks, the first instruction of the block is reachable, so we
+ // only need to determine reachability between whole blocks.
+
+ const BasicBlock *BB = A->getParent();
+ // If the block is in a loop then we can reach any instruction in the block
+ // from any other instruction in the block by going around the backedge.
+ // Check whether we're in a loop (or aren't sure).
+
+ // Can't be in a loop if it's the entry block -- the entry block may not
+ // have predecessors.
+ bool HasLoop = BB != &BB->getParent()->getEntryBlock();
+
+ // Can't be in a loop if LoopInfo doesn't know about it.
+ if (LI && HasLoop) {
+ HasLoop = LI->getLoopFor(BB) != 0;
+ }
+ if (HasLoop)
+ return true;
+
+ // Linear scan, start at 'A', see whether we hit 'B' or the end first.
+ for (BasicBlock::const_iterator I = A, E = BB->end(); I != E; ++I) {
+ if (&*I == B)
+ return true;
+ }
+ return false;
+}
+
+bool llvm::isPotentiallyReachable(const Instruction *A, const Instruction *B,
+ DominatorTree *DT, LoopInfo *LI) {
+ assert(A->getParent()->getParent() == B->getParent()->getParent() &&
+ "This analysis is function-local!");
+
+ const BasicBlock *StopBB = B->getParent();
+
+ if (A->getParent() == B->getParent())
+ return isPotentiallyReachableSameBlock(A, B, LI);
+
+ if (A->getParent() == &A->getParent()->getParent()->getEntryBlock())
+ return true;
+ if (B->getParent() == &A->getParent()->getParent()->getEntryBlock())
+ return false;
+
+ // When the stop block is unreachable, it's dominated from everywhere,
+ // regardless of whether there's a path between the two blocks.
+ if (DT && !DT->isReachableFromEntry(StopBB))
+ DT = 0;
+
+ // Limit the number of blocks we visit. The goal is to avoid run-away compile
+ // times on large CFGs without hampering sensible code. Arbitrarily chosen.
+ unsigned Limit = 32;
+
+ SmallSet<const BasicBlock*, 64> Visited;
+ SmallVector<BasicBlock*, 32> Worklist;
+ Worklist.push_back(const_cast<BasicBlock*>(A->getParent()));
+
+ do {
+ BasicBlock *BB = Worklist.pop_back_val();
+ if (!Visited.insert(BB))
+ continue;
+ if (BB == StopBB)
+ return true;
+ if (DT && DT->dominates(BB, StopBB))
+ return true;
+ if (LI && loopContainsBoth(LI, BB, StopBB))
+ return true;
+
+ if (!--Limit) {
+ // We haven't been able to prove it one way or the other. Conservatively
+ // answer true -- that there is potentially a path.
+ return true;
+ }
+
+ if (const Loop *Outer = LI ? getOutermostLoop(LI, BB) : 0) {
+ // All blocks in a single loop are reachable from all other blocks. From
+ // any of these blocks, we can skip directly to the exits of the loop,
+ // ignoring any other blocks inside the loop body.
+ Outer->getExitBlocks(Worklist);
+ } else {
+ for (succ_iterator I = succ_begin(BB), E = succ_end(BB); I != E; ++I)
+ Worklist.push_back(*I);
+ }
+ } while (!Worklist.empty());
+
+ // We have exhaustived all possible paths and are certain that 'To' can not
+ // be reached from 'From'.
+ return false;
+}